1. Field of the Invention
The present invention relates to a method of producing a material (hereinafter referred to "mold material") used for forming a metallic mold body and the material obtained by the method. Particularly, the invention relates to a method of producing a material used for forming the body which has open pores over the entire wall of the body and which is, for example, used in metal casting or plastics molding.
2. Description of Related Art
The bodies of metal molds used in metal casting or plastics molding are generally formed through the steps of melting, casting and machining. The applicant of the present invention has previously proposed a mold material which is different from the materials obtained by conventional methods (JP-A-2-101102). The mold material contains short steel fibers each having an aspect ratio (.mu./d) of 30 to 100 and a width of 100 .mu.m or less.
Such short steel fibers are produced by a wire cutting method known as a method of cutting a steel wire to a thin flat form along the lengthwise direction. Long fibers obtained by the method are cut into short fibers having an aspect ratio (l/d: l is the fiber length; d is the width of a fiber) of 30 to 100.
0.5 to 1.2 wt % of carbon powder and, if required, chromium powder and/or manganese powder are blended with the short steel fibers to obtain a blended material. The blended material is crammed, with a uniform density, into a press forming mold or a CIP (Cold Isostatic Press) rubber (for example, urethane rubber or neoprene rubber) mold and compressed at a pressure of 0.5 to 8 ton/cm.sup.2. The thus obtained molded product is sintered in a reducing atmosphere to form a desired mold material.
The mold material has excellent strength and toughness and need not to be subjected to form air vent holes which are required in conventional molds made of tool steel because the mold material has already open pores which are uniformly distributed over the entire body. However, the mold material has a defect that the open pores are blocked up due to generation of rust, which is caused by oxidative corrosion of the short steel fibers in the material during use. The mold material also has a poor wear resistance because of low hardness.